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How Extreme Heat Affects Corn and Soybeans

    How Extreme Heat Affects Corn and Soybeans

    With temperatures in the triple digits this summer, grain crop growers must understand how heat impacts plants. For starters, human concepts such as heat index and feelings do not apply to plants. Instead, heat affects people and plants differently.

    Plants care more about leaf temperature than the air temperature. Leaves absorb light to produce sugars and other nutrients required for life and yield. Plants consume only a tiny portion of the available light energy. Extra energy raises the temperature of the leaf.

    Converting water from liquid to vapor consumes significant energy and results in a cooling impact. If the air temperature is lower than the leaf temperature, conduction occurs when the warm leaf surface returns energy to the air that touches it. Cooler air flows closer to the leaf’s surface and displaces warmer air through convection.

    Wiebold claims that temperature has a direct impact on yield potential. Enzymes (proteins) regulate the chemical reactions required for plants to survive. Temperature increases the rate of these processes. For example, plant growth and weight gain are more significant at 80°F than at 50°F. In addition, plant enzymes’ three-dimensional structures can twist or change at high temperatures.

    An egg frying is an extreme illustration of how temperature affects protein. Heat causes the egg protein to harden and alter its form. Although less striking, elevated leaf temperatures change the structure of plant enzymes, impairing their function.

    Agronomists believe that 86°F is the ideal temperature for maize and soybean development. However, temperatures above 86°F impede essential reactions, including photosynthesis, limiting yield potential.

    Leaf temperatures are frequently greater than air temperatures during the day, especially on bright, sunny days with minimal wind. This is because evaporation occurs quickly enough with an adequate moisture supply to keep leaf temperatures close to air temperature. However, water may evaporate later, sufficient to chill the leaf if there is a lack of moisture. This raises the temperature of the leaf. Therefore, when air temperatures are high, conduction and convection are ineffective at moving heat away from the leaf.

    Plants react to the stress of high leaf temperatures in various ways. Corn leaves, for example, wrap into a cylinder to limit the leaf surface exposure to light. The leaves also lean upward. Plants with broad leaves, such as soybean, do not roll. Instead, they align their flat leaves with the oncoming sunshine.

    If heat stress persists, soybeans and other broadleaf plants will rotate their leaves so that the lighter-colored bottom surfaces face upward, allowing light to reflect. This lowers the temperature of the leaf and limits its exposure to sunlight. In addition, lowering leaf temperature reduces water evaporation.

    In most years, the direct effect of high temperatures on crop production is minor. However, when temperatures exceed 95°F, as frequently this summer, maize, and soybean yields may suffer, even in the few places of Missouri where significant precipitation was received.

    High temperatures have a less noticeable effect on photosynthesis and respiration. Photosynthesis is a source of income for plants, while respiration is a source of expense. The difference is net photosynthesis, which equals net income. Within limits, robust net photosynthesis yields a high yield.

    Plants require respiration to burn carbohydrates and generate energy for various biological activities. Some respiration, however, is squandered because it burns or oxidizes carbohydrates that could be stored in seeds as yield. High temperatures promote respiration over photosynthesis, reducing the plant’s net revenue. This is especially true at night when there is no photosynthesis. Warm evenings reduce production without affecting the plants.

    The phrase has no meaning for plants. Plants benefit from high midday humidity because lesser evaporation decreases water stress. The rate at which air temperatures fall is slowed by high evening humidity. When humidity is high (dew point above 70°F.), it is not uncommon for temperatures to persist above 80°F on summer nights. Although plants do not experience a high heat index, the sluggish temperature decrease during high-humidity nights is reflected in higher respiration.

    It is difficult to distinguish between extreme heat’s consequences and water stress symptoms. These two pressures frequently coexist and amplify one other’s impacts. However, extreme temperatures can lower production even if plants exhibit no signs of water stress.

    Learn more: How to Defend Your Farm Against Corn Rootworm